Pulse tube refrigeration without moving parts, operating at cryogenic temperature, is one attractive method for providing a reliable, vibration-free, long life, and simple cryocooler that can meet the requirements for cryogenic cooling in many applications. In order to produce cooling effect at a pulse tube cold end, it is necessary to cause a time-phasing [shifting] between gas pressure fluctuations and gas displacement inside the pulse tube. Such phase shift between the gas pressure fluctuation and the gas displacement inside the pulse tube is obtained by controlling the mass flow rate with a phase shifter located at the pulse tube warm end.
Several types of phase shifters have been developed for improvement in performance of the pulse tube refrigerator, such as double inlet, four valve, and active buffer type phase shifters. However, there are several disadvantages in present phase shifters for multiple stage pulse tube refrigerators.
In the double inlet type and four valve pulse tube refrigerator for producing large cooling capacity at relatively high temperature, a large amount of additional compressor work is expended due to mass flow in and out of a bypass line and valves. This added workload decreases overall efficiency of the machine. In multiple stage double inlet and four valve pulse tube refrigerators, phase interaction between each stage produces thermal losses and makes the refrigeration temperature unstable at each stage.
In the active buffer type pulse tube refrigerator producing small cooling capacity at very low temperature, regenerator inefficiency is very high due to larger mass flow rate through the regenerator cold end and poor phase shift effect at a higher ratio of regenerator void volume to pulse tube volume.